1. Field of the Invention
The invention relates to a process for the preparation of dialkyl carbonates by reacting alkylene oxides with alcohols and carbon dioxide in the presence of catalysts.
2. Discussion of the Prior Art
It is surprising that dialkyl carbonates can be prepared at all by reacting alkylene oxides with alcohols and carbon dioxide.
Rather, it was to be expected that polymerisation reactions which lead, for example, to polycarbonates and polyglycols take place in the reaction of alkylene oxides with alcohols and carbon dioxide.
It is known, in fact, from U.S. Pat. Nos. 3,248,415 and 3,248,416 that alkylene oxides and carbon dioxide or alkylene oxides, carbon dioxide and glycol carbonates react in the presence of small amounts of diglycols or polyglycols, under the catalytic influence of bases, to give polycarbonates which, however, predominantly contain polyalkylene oxide units and therefore in the strict sense are to be considered polyether-polycarbonates.
Furthermore, it is known from Makromol. Chem. 130, 210 (1969) that in the reaction of alkylene oxides with carbon dioxide in the presence of zinc diethyl as the catalyst, large amounts of polyglycols are obtained in addition to small amounts of alternating copolymers of alkylene oxides and carbon dioxide.
In addition to the polymerisation reactions, the formation of alkyl glycol ethers was to be expected as a side reaction. Because of the large number of hydroxyl groups present, amounts of alcohols equivalent to the amounts of alkylene oxide are added. Thus, the alkylene oxide should react with the alcohol to a considerable degree to give alkyl glycol ethers.